A simple conventional conducting cable comprises a length of conductive material having a circular cross section, or several such conductors wound or plaited together, the conductor or conductors being wrapped in a insulating sheath. In locations such as the surface of the sea bed, and the borehole of an oil well, several insulating layers and armored layers may be included.
When it is desired to supply power or to carry data from the bottom of a borehole, the conducting cable may either be strapped to the outside of the drillpipe or coiled tubing, or attached to the inside. Attaching the cable to the inside of a drill string or a length of coiled tubing is difficult, as in most methods some form of joining has to take place. This is especially difficult in the case of coiled tubing, as it is difficult to access the joining points over the entire continuous long length of the tube. Known techniques include remotely activatable securement devices attached at intervals along the cable.
It is comparatively simple to strap the conductive cable to the outside of the drill string or tubing, since the outside is freely accessible, but the cable is then prone to damage due to the harsh environment, and the mechanical wear produced by the movement of the drill string through the borehole.
Similar problems occur when including a conductive cable while laying pipelines upon the surface of the sea bed.